1. Field of the Invention
This invention relates to an electrodynamic loudspeaker suitable for use in low, medium and high range audio frequencies having substantially hemispherical sound emission characteristics.
2. Description of the Prior Art
In recent years, audio systems have reached a remarkable level of evolution. However loudspeakers, the last step in the process of converting electrical signals to sound, have not had notorious changes although worldwide manufacturers are encouraged to develop significant improvements to satisfy the most demanding market. For instance, one particular concern is to design a full range loudspeaker with wide dispersion of sound.
Presently, it is standard to use a woofer for low frequency signals; A mid range for medium frequency signals in which the human voice is ranged and the hearing sense analyzes sound waves by comparison of phases in each ear and by the intensity of the signals, thus producing the stereophonic effect; And finally a tweeter for high frequency signals. But for high frequencies, traveling sound waves are very directional, reason why tweeters utilize sound dispersion devices that include sound deflectors.
For medium range audio frequencies it is not possible to build a system that utilizes sound deflectors to broaden the sound dispersion without causing undesired interference effects on acoustic waves of certain frequencies, and it is precisely the wider or narrower sound dispersion what determines the most adequate area for stereophonic listening.
In order to provide background information so that the invention may be completely understood and appreciated in its proper context, reference is made to a number of prior art patents and publications as follows:
An advertisement on page 23 of Radio Electronics, November 1990, presents a new technique by restoration of certain frequencies in recorded audio to obtain a new kind of sound that would replace the effect of multiple speaker arrays.
Such new kind of sound is due to improvements in the amplifier circuitry being not related to speaker systems, limited to certain applications.
U.S. Pat. No. 4,881,265 discloses a system combining two tweeters and two woofers mounted in apex cabinet at an angle of 70.degree., duplicating the angle of dispersion of a single tweeter.
According to the assembly, however, the angle of dispersion increases only in the horizontal plane while the vertical plane remains unaffected.
U.S. Pat. No. 3,720,787 discloses a globular speaker system with omnidirectional characteristics constituted by a plurality of speakers attached to a spherical baffle.
The main disadvantage of this device is its structural complexity, and to overcome acoustic interference effects in certain frequencies.
U.S. Pat. No. 3,456,755 discloses two hydraulic loudspeakers arranged in a sphere for omnidirectional dispersion of sound, and it is said that this device operates on the principle that a liquid under pressure exert equal force in all directions so that a diaphragm subjected to the fluctuations of pressure incidental to the movement of a voice coil carrying a signal will respond in a uniform manner over its entire surface.
The coupling between voice coil and diaphragm is not by rigid means, since vibrations are transmitted through liquid. Matching the acoustic impedances between the liquid means and the air for all audio frequencies is very difficult.
U.S. Pat. No. 4,472,605 discloses two hemispherical diaphragms each one arranged on either side of a disc-shaped carrier forming a sphere to radiate sound in all directions.
It is designed for low and mid range frequencies only. Even for low frequencies its limitation lies in the undesired effects caused by the small amount of air volume between diaphragms in the interior of the loudspeaker and also in the fact that toward the edge of the hemispherical diaphragm vibrations radiated become weaker as the lines tangent to that part of the hemispherical diaphragm and the voice coil carrier axis tend to parallels.
U.S. Pat. No. 4,665,550 discloses an electrodynamic loudspeaker having omnidirectional sound emission in high or medium frequency. Therefore, it cannot be a full range loudspeaker.
Whatever the advantages and features of the above cited references, none of them fulfills the objects of the present invention.